The present invention relates to an automatic locking type cutter knife. The automatic locking type cutter knife is known to have a variety of operations and structures. The automatic locking type cutter knife, as disclosed in Examined Published Japanese Utility Model Application No. 57-54771 or 61-35177, is equipped with a stopper mounted on the back face of the center protruding portion of a retaining leaf spring for preventing the leaf spring from turning. This structure can prevent the turning of the leaf spring when the stopper is moved in one direction. When the spring is released, it is troublesome to return the stopper. When a force acts to move a slider to be coupled to a cutter blade while the slider is being retained by the stopper, the center protruding portion of the leaf spring is pushed forward or backward onto the square hole of a blade holder. As a result, the center protruding portion of the leaf spring is pushed so much between the square hole and the corrugated ridge of the knife frame that it is unusably deformed.
On the other hand, an automatic locking type cutter knife, as disclosed in Unexamined Published Japanese Patent Application No. 6-327849, employs a leaf spring having a generally triangular projecting portion for a triangular engaging groove. This structure raises a problem in the reliability of the retaining force of the cutter blade. Another problem is that the leaf spring is liable to come out from the opening of a center recess, as formed in a body member of the slider, and to be deformed.
In an automatic locking type cutter knife, as disclosed in Examined Published Japanese Patent Application No. 7-85752, a leaf spring is provided with a flat spring portion extending in the forward direction of a cutter blade, and a protruding portion having an inverted U-shaped section and protruding at a right angle with respect to the spring portion. This structure has a problem that the force to be applied by the leaf spring to an engaging groove is weak in a neutral position.
The invention has been conceived with a view to the background thus far described and has an object to provide a cutter knife which can be stepwise automatically locked while preventing the leaf spring from being unusably deformed.